Silent proactive handoff

ABSTRACT

In some embodiments, a silent proactive handoff is performed wherein a mobile device that is using a current network to transport its application traffic uses its silent periods to connect to at least one target network temporarily and uses this temporary connectivity to perform actions needed for handoff into the target network. Among other things, with such a silent proactive handoff approach, e.g., if handoff actions to a target network fail during silent periods, there can still be essentially no impact on the applications.

BACKGROUND

1. Field of the Invention

The present application relates to wireless networking and, in somepreferred embodiments, to methods of improving handoff of a mobiledevice between neighboring networks and/or the like.

2. General Background Discussion

Networks and Internet Protocol

There are many types of computer networks, with the Internet having themost notoriety. The Internet is a worldwide network of computernetworks. Today, the Internet is a public and self-sustaining networkthat is available to many millions of users. The Internet uses a set ofcommunication protocols called TCP/IP (i.e., Transmission ControlProtocol/Internet Protocol) to connect hosts. The Internet has acommunications infrastructure known as the Internet backbone. Access tothe Internet backbone is largely controlled by Internet ServiceProviders (ISPs) that resell access to corporations and individuals.

With respect to IP (Internet Protocol), this is a protocol by which datacan be sent from one device (e.g., a phone, a PDA [Personal DigitalAssistant], a computer, etc.) to another device on a network. There area variety of versions of IP today, including, e.g., IPv4, IPv6, etc.Each host device on the network has at least one IP address thatidentifies the host device's point of attachment to the IP networks.

IP is a connectionless protocol. The connection between end pointsduring a communication is not continuous. When a user sends or receivesdata or messages, the data or messages are divided into components knownas packets. Every packet is treated as an independent unit of data.

In order to standardize the transmission between points over theInternet or the like networks, an OSI (Open Systems Interconnection)model was established. The OSI model separates the communicationsprocesses between two points in a network into seven stacked layers,with each layer adding its own set of functions. Each device handles amessage so that there is a downward flow through each layer at a sendingend point and an upward flow through the layers at a receiving endpoint. The programming and/or hardware that provides the seven layers offunction is typically a combination of device operating systems,application software, TCP/IP and/or other transport and networkprotocols, and other software and hardware.

Typically, the top four layers are used when a message passes from or toa user and the bottom three layers are used when a message passesthrough a device (e.g., an IP host device). An IP host is any device onthe network that is capable of transmitting and receiving IP packets,such as a server, a router or a workstation. Messages destined for someother host are not passed up to the upper layers but are forwarded tothe other host. In the OSI and other similar models, IP is in Layer-3,the network layer. The layers of the OSI model are listed below.

Layer 7 (i.e., the application layer) is a layer at which, e.g.,communication partners are identified, quality of service is identified,user authentication and privacy are considered, constraints on datasyntax are identified, etc.

Layer 6 (i.e., the presentation layer) is a layer that, e.g., convertsincoming and outgoing data from one presentation format to another, etc.

Layer 5 (i.e., the session layer) is a layer that, e.g., sets up,coordinates, and terminates conversations, exchanges and dialogs betweenthe applications, etc.

Layer-4 (i.e., the transport layer) is a layer that, e.g., managesend-to-end control and error-checking, etc.

Layer-3 (i.e., the network layer) is a layer that, e.g., handles routingand forwarding, etc.

Layer-2 (i.e., the data-link layer) is a layer that, e.g., providessynchronization for the physical level, does bit-stuffing and furnishestransmission protocol knowledge and management, etc. The Institute ofElectrical and Electronics Engineers (IEEE) sub-divides the data-linklayer into two further sub-layers, the MAC (Media Access Control) layerthat controls the data transfer to and from the physical layer and theLLC (Logical Link Control) layer that interfaces with the network layerand interprets commands and performs error recovery.

Layer 1 (i.e., the physical layer) is a layer that, e.g., conveys thebit stream through the network at the physical level. The IEEEsub-divides the physical layer into the PLCP (Physical Layer ConvergenceProcedure) sub-layer and the PMD (Physical Medium Dependent) sub-layer.

Typically, layers higher than layer-2 (such as, e.g., layers includingthe network layer or layer-3 in the OSI model and the like) are referredto as the higher-layers.

Wireless Networks

Wireless networks can incorporate a variety of types of mobile devices,such as, e.g., cellular and wireless telephones, PCs (personalcomputers), laptop computers, wearable computers, cordless phones,pagers, headsets, printers, PDAs, etc. For example, mobile devices mayinclude digital systems to secure fast wireless transmissions of voiceand/or data. Typical mobile devices include some or all of the followingcomponents: a transceiver (i.e., a transmitter and a receiver,including, e.g., a single chip transceiver with an integratedtransmitter, receiver and, if desired, other functions); an antenna; aprocessor; one or more audio transducers (for example, a speaker or amicrophone as in devices for audio communications); electromagnetic datastorage (such as, e.g., ROM, RAM, digital data storage, etc., such as indevices where data processing is provided); memory; flash memory; a fullchip set or integrated circuit; interfaces (such as, e.g., USB, CODEC,UART, PCM, etc.); and/or the like.

Wireless LANs (WLANs) in which a mobile user can connect to a local areanetwork (LAN) through a wireless connection may be employed for wirelesscommunications. Wireless communications can include, e.g.,communications that propagate via electromagnetic waves, such as light,infrared, radio, microwave. There are a variety of WLAN standards thatcurrently exist, such as, e.g., Bluetooth, IEEE 802.11, and HomeRF.

By way of example, Bluetooth products may be used to provide linksbetween mobile computers, mobile phones, portable handheld devices,personal digital assistants (PDAs), and other mobile devices andconnectivity to the Internet. Bluetooth is a computing andtelecommunications industry specification that details how mobiledevices can easily interconnect with each other and with non-mobiledevices using a short-range wireless connection. Bluetooth creates adigital wireless protocol to address end-user problems arising from theproliferation of various mobile devices that need to keep datasynchronized and consistent from one device to another, thereby allowingequipment from different vendors to work seamlessly together. Bluetoothdevices may be named according to a common naming concept. For example,a Bluetooth device may possess a Bluetooth Device Name (BDN) or a nameassociated with a unique Bluetooth Device Address (BDA). Bluetoothdevices may also participate in an Internet Protocol (IP) network. If aBluetooth device functions on an IP network, it may be provided with anIP address and an IP (network) name. Thus, a Bluetooth Device configuredto participate on an IP network may contain, e.g., a BDN, a BDA, an IPaddress and an IP name. The term “IP name” refers to a namecorresponding to an IP address of an interface.

An IEEE standard, IEEE 802.11, specifies technologies for wireless LANsand devices. Using 802.11, wireless networking may be accomplished witheach single base station supporting several devices. In some examples,devices may come pre-equipped with wireless hardware or a user mayinstall a separate piece of hardware, such as a card, that may includean antenna. By way of example, devices used in 802.11 typically includethree notable elements, whether or not the device is an access point(AP), a mobile station (STA), a bridge, a PCMCIA card or another device:a radio transceiver; an antenna; and a MAC (Media Access Control) layerthat controls packet flow between points in a network.

In addition, Multiple Interface Devices (MIDs) may be utilized in somewireless networks. MIDs may contain two or more independent networkinterfaces, such as a Bluetooth interface and an 802.11 interface, thusallowing the MID to participate on two separate networks as well as tointerface with Bluetooth devices. The MID may have an IP address and acommon IP (network) name associated with the IP address.

Wireless network devices may include, but are not limited to Bluetoothdevices, Multiple Interface Devices (MIDs), 802.11x devices (IEEE 802.11devices including, e.g., 802.11a, 802.11b and 802.11g devices), HomeRF(Home Radio Frequency) devices, Wi-Fi (Wireless Fidelity) devices, GPRS(General Packet Radio Service) devices, 3G cellular devices, 2.5Gcellular devices, GSM (Global System for Mobile Communications) devices,EDGE (Enhanced Data for GSM Evolution) devices, TDMA type (Time DivisionMultiple Access) devices, or CDMA type (Code Division Multiple Access)devices, including CDMA2000. Each network device may contain addressesof varying types including but not limited to an IP address, a BluetoothDevice Address, a Bluetooth Common Name, a Bluetooth IP address, aBluetooth IP Common Name, an 802.11 IP Address, an 802.11 IP commonName, or an IEEE MAC address.

Wireless networks can also involve methods and protocols found in, e.g.,Mobile IP (Internet Protocol) systems, in PCS systems, and in othermobile network systems. With respect to Mobile IP, this involves astandard communications protocol created by the Internet EngineeringTask Force (IETF). With Mobile IP, mobile device users can move acrossnetworks while maintaining their IP Address assigned once. See Requestfor Comments (RFC) 3344. NB: RFCs are formal documents of the InternetEngineering Task Force (IETF). Mobile IP enhances Internet Protocol (IP)and adds means to forward Internet traffic to mobile devices whenconnecting outside their home network. Mobile IP assigns each mobilenode a home address on its home network and a care-of-address (CoA) thatidentifies the current location of the device within a network and itssubnets. When a device is moved to a different network, it receives anew care-of address. A mobility agent on the home network can associateeach home address with its care-of address. The mobile node can send thehome agent a binding update each time it changes its care-of addressusing, e.g., Internet Control Message Protocol (ICMP).

In basic IP routing (i.e. outside mobile IP), typically, routingmechanisms rely on the assumptions that each network node always has aconstant attachment point to, e.g., the Internet and that each node's IPaddress identifies the network link it is attached to. In this document,the terminology “node” includes a connection point, which can include,e.g., a redistribution point or an end point for data transmissions, andwhich can recognize, process and/or forward communications to othernodes. For example, Internet routers can look at, e.g., an IP addressprefix or the like identifying a device's network. Then, at a networklevel, routers can look at, e.g., a set of bits identifying a particularsubnet. Then, at a subnet level, routers can look at, e.g., a set ofbits identifying a particular device. With typical mobile IPcommunications, if a user disconnects a mobile device from, e.g., theInternet and tries to reconnect it at a new subnet, then the device hasto be reconfigured with a new IP address, a proper netmask and a defaultrouter. Otherwise, routing protocols would not be able to deliver thepackets properly.

Handoffs of Mobile Devices

In the context of, for example, a mobile device with an IP-basedwireless network interface (such as, e.g., an IEEE 802.11 or an 802.16interface), the mobile device needs to perform roaming or handoffs whenit moves from one network into another network. With existing handoffmethodologies, handoff is typically accomplished by performing thefollowing sequence of protocol layer specific handoffs:

-   -   First, handoff takes place at the physical layer. In this        regard, the mobile device switches its radio channel to, e.g., a        wireless base station or wireless access point in the target        network.    -   Second, handoff takes place at layer-2. In this regard, the        mobile device switches its layer-2 (i.e., link-layer)        connections to the target network. As explained above, the link        layer or layer-2 refers to the protocol immediately below the        IP-layer that carries user traffic. The mobile device performs        layer-2 authentication with the target network if the target        network requires such authentication.    -   Third, handoff takes place at the IP-layer. In this regard, the        mobile device obtains a local IP address from the target        network, performs IP-layer authentication if required by the        target network, and then performs IP-layer location update so        that IP packets destined to the mobile device can be routed by        the IP network to the mobile device via the target network. In        some instances, one way to support IP layer location update is        to use Mobile IP defined by the Internet Engineering Task Force        (IETF).    -   Forth, handoff takes place at the application-layer. The mobile        device performs necessary steps at the application layer to        ensure that its application traffic will flow correctly to the        applications on the mobile device via the target network. For        example, when the mobile device uses the Session Initiation        Protocol (SIP) defined by the IETF to manage its        application-layer signaling, an application layer handoff can be        achieved by the mobile device updating its current location with        its home SIP server. The mobile device may also need to carry        out application-layer authentication with the target network if        required by the target network. This is the case, for example,        when the mobile device is using the IP Multimedia Subsystem        (IMS) in a visited 3GPP (3^(rd) Generation Partnership Project)        wireless network, where the IMS is a SIP-based system supporting        application-layer signaling and management for multimedia        applications over 3GPP networks.

Sometimes, either IP-layer handoff or application-layer handoff issufficient. That is, it may be unnecessary to perform both IP-layer andapplication-layer handoff. These existing methods can lead tosignificant handoff delays when they are used in IP-based wirelessnetworks. For example, in a geographical region where there are manywireless local area networks (WLANs) such as in cities, inside buildingcomplexes or residential homes, or in other public places where multiplewireless LANs exist, a mobile device may receive strong radio signalsfrom multiple radio networks at the same time. However, the mobiledevice may not be authorized to use some of these radio networks.

Under the existing handoff methods described above, a mobile device willselect a target network based on, for example, radio signal strengths,and will go through the steps described above to connect to the targetnetwork and then discover, for example, if it is authorized to use thenetwork or if the network does not provide the capabilities (e.g.,sufficient available bandwidth) or the services that the mobile deviceneeds. Consequently, the mobile device will have to try to connect toanother network, and will repeat this process until it finally connectsto a network that provides and that allows it to use the capabilitiesand services it needs (or until it has exhausted all possible networks).Accordingly, with existing systems, a handoff can take a long time thatcan be intolerable and can delay sensitive applications such as, as someexamples, live voice and/or video applications.

While a variety of systems and methods are known, there remains a needfor improved systems and methods for performing handoffs in wirelessnetworks.

SUMMARY OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the present invention can significantlyimprove upon existing systems and methods for performing handoffs inwireless networks.

In some embodiments, a silent proactive handoff is performed wherein amobile device that is using a current network to transport itsapplication traffic uses its silent periods to connect to at least onetarget network temporarily and uses this temporary connectivity toperform actions needed for handoff into the target network. Among otherthings, with such a silent proactive handoff approach, e.g., if handoffactions to a target network fail during silent periods, there can stillbe essentially no impact on the applications.

According to some preferred embodiments, a method for performing silentproactive handoff of a mobile device to a target network while themobile device is using a current network is performed that includes:while the mobile device is using the current network to transportapplication traffic and the current network satisfies the mobiledevice's requirements, having the mobile device use at least one silentperiod to temporarily connect to at least one target network toproactively perform at least one handoff action for potential laterhandoff to the target network.

Preferably, the method further includes that the mobile device sends orreceives substantially no traffic over the current access network duringthe at least one silent period. In addition, the method preferablyincludes having the mobile device use the at least one silent period toconnect to the target network so that the mobile device receivesadvertisement messages from the target network. In some embodiments, themethod further includes having the mobile device use the at least onesilent period to establish a layer-2 connection or association with thetarget network for receiving IP-layer or high layer advertisements fromthe target network. In some embodiments, the method includes having themobile device use the at least one silent period to perform layer-2,layer-3 or application layer authentication with the target network.Preferably, the method includes having the mobile device perform thefollowing handoff actions during the at least one silent period: a)discovering neighboring network information; b) obtaining a local IPaddress from the target network; and c) performing authentication withthe target network.

In some other embodiments, the method includes having the mobile devicedetermine if the at least one silent period is sufficient to completeone or more handoff action. For example, the method may include havingthe mobile device determine if the at least one silent period issufficient to complete one or more handoff action by comparison to apre-set or a dynamically determined threshold.

In some preferred embodiments, the method further includes having themobile device predict an actionable silent period based on monitoring oftime periods and a prediction model. In some examples, the methodincludes dynamically estimating at least one actionable silent periodthreshold for at least one handoff action based on previous times themobile device took to perform handoff actions, using the at least onethreshold and inter-packet times determined from a traffic monitor todetect a next silent period, to predict if this next silent period willbe an actionable silent period, and to predict a length of the nextactionable silent period.

In some preferred embodiments, the method further includes having themobile device select a target network to which the mobile may switch to.Preferably, the method includes when a target network is selected and anactionable silent period is detected, switching the mobile device'slayer-2 connection to the target network. In some embodiments, themethod includes having the mobile device connect successfully to thetarget network and before a current actionable silent period expires,having the mobile device enter an information discovery phase to listento the target network's advertisement messages to learn informationneeded to perform handoffs at different protocol layers to the targetnetwork, and if the current actionable silent period has not expiredafter the information discovery phase, having the mobile device start atleast one handoff action.

In some embodiments, the method includes after having the mobile devicestart the at least one handoff action, in the event that the currentnetwork continues to satisfy the mobile device's requirements, havingthe mobile device switch its network connection back to the currentnetwork. In some embodiments, the method includes after having themobile device start the at least one handoff action, in the event thatthe current network does not continue to satisfy the mobile device'srequirements, having the mobile device perform the remaining handoffsteps to finish a handoff. In some embodiments, the method includeshaving the mobile device make a determination as to whether to utilize asilent proactive handoff based on an estimation of the time that themobile device will be within a candidate network. In some exemplaryembodiments, the method further includes having the mobile device makethe determination based on one or more of the following parameters:types of user applications; relative speed at which the mobile device ismoving; and a predicted size of a candidate network.

According to some other embodiments of the invention, a mobile devicehaving silent proactive handoff capability is provided that includes: atraffic monitor component configured to monitor time periods betweenpackets transmitted to or from the mobile device over a current accessnetwork; a target network selector component configured to select atarget network to which the mobile device may potentially switch to; asilence predictor component configured to predict an actionable silenceperiod; and a silent handoff controller configured to control a silentproactive handoff to a target network during the actionable silentperiod. Preferably, the silent handoff controller is configured toestablish connections to a target network, to discover networkinformation about a target network, to obtain a local IP address for themobile device from the target network, and to perform authenticationwith the target network.

The above and/or other aspects, features and/or advantages of variousembodiments will be further appreciated in view of the followingdescription in conjunction with the accompanying figures. Variousembodiments can include and/or exclude different aspects, featuresand/or advantages where applicable. In addition, various embodiments cancombine one or more aspect or feature of other embodiments whereapplicable. The descriptions of aspects, features and/or advantages ofparticular embodiments should not be construed as limiting otherembodiments or the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The preferred embodiments of the present invention are shown by a way ofexample, and not limitation, in the accompanying figures, in which:

FIG. 1 is a flow diagram illustrating some steps of an exemplaryembodiment of a silent proactive handoff approach according to someembodiments of the present invention;

FIG. 2 is a schematic diagram depicting the structure of an actionablesilent period predictor according to some embodiments of the presentinvention;

FIG. 3 is a schematic diagram demonstrating the use of silent periodsfor network discovery and for performing proactive handoff actions;

FIG. 4 is an architectural diagram showing components of a mobile deviceaccording to some illustrative embodiments of the invention; and

FIG. 5 is an architectural diagram showing movement of a mobile devicealong a path traversing a plurality of wireless networks forillustrative purposes.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

While the present invention may be embodied in many different forms, anumber of illustrative embodiments are described herein with theunderstanding that the present disclosure is to be considered asproviding examples of the principles of the invention and that suchexamples are not intended to limit the invention to preferredembodiments described herein and/or illustrated herein.

According to the preferred embodiments of the invention, a new approachis used to significantly reduce the handoff delays, which approach isreferred to herein as Silent Proactive Handoff (SPH). In some preferredembodiments, a silent proactive handoff operates as follows: when amobile is using one network (referred to as the old network or thecurrent network) to transport its application traffic and this networkcan satisfy the mobile device's requirements, the mobile device uses itssilent periods to connect to one or more target neighboring network(s)temporarily (i.e., only during these silent periods) and uses thistemporary connectivity to perform actions needed for handoff into thetarget network.

In the preferred embodiments, a silent period is a time period duringwhich the mobile has no traffic to send or receive over the currentaccess network. In some embodiments, a silent period can be defined as atime period during which the mobile has substantially no traffic to sendor receive. In preferred embodiments, during a silent period, a mobiledevice would not be expecting incoming traffic at the IP and higherprotocol layers. Moreover, in preferred embodiments, the mobile devicewill not control if and/or when there may be incoming traffic, but themobile device will predict or estimate silent periods. Thus, inpreferred embodiments, a silent period is a time period during which themobile device does not need to send or receive IP or higher layertraffic (e.g., not just application layer traffic). In some instances,the mobile device may send traffic at protocol layers below the IP layerduring a silent period. In addition, in some examples, a silent periodcan include time periods during which the mobile device may send orreceive only certain IP layer or higher layer traffic (such as, e.g.,application layer traffic) which, when temporarily interrupted (e.g.,delayed or discarded), will substantially not cause undesirable orunexpected effects to the user of a mobile device.

When a mobile device is inside overlapping radio coverage areas ofmultiple radio networks, existing network interface cards can receiveradio beacons from these radio networks simultaneously. These radiobeacons, however, do not provide IP or higher layer information, suchas, e.g., IP addresses of the access IP routers, IP address allocationservers (e.g., DHCP servers), or authentication servers inside a targetnetwork, and do not provide the necessary IP and higher layer parametervalues necessary to connect to or authenticate with a target network.

According to preferred embodiments, with a novel silent proactivehandoff approach, the mobile device uses the silent periods to connectto a target network so that the mobile device can receive, e.g.,IP-layer and/or high layer advertisement messages from the targetnetwork. Since these advertisement packets are typically broadcast overthe local IP sub-networks, receiving these advertisement packets from atarget network generally does not require the mobile device to obtain alocal IP address from the target network.

Depending on the specific types of the radio networks, the mobile devicemay need to establish a layer-2 connection or an association to thetarget network for receiving IP-layer or high layer advertisements fromthe target network. In some embodiments, establishing a layer-2connection to a target network may require the mobile device to performlayer-2 authentication with the target network if the target networkimplements layer-2 authentication mechanisms.

In this disclosure, the terminology “connected to a target network”refers to the establishment of the necessary connection or associationwith a target network to the extent that the mobile can receive IP-layerand/or high layer advertisement messages. Once connected to a targetnetwork, the mobile can perform a range of actions during the silentperiod that need to be done during an actual handoff. In someembodiments, these actions can include some or all of the following:

-   -   Neighboring network information discovery: This may be done to        discover the information needed by the mobile to handoff into        the neighboring network. To do so, the mobile device can listen        to advertisements at layer-2, the IP-layer and/or the        application layer from the target network to obtain information        regarding the target network. This information may include,        e.g., the addresses of the access IP routers, addresses of the        IP address allocation servers (e.g., Dynamic Host Configuration        Protocol (DHCP) servers), addresses of the authentication        routers, and other parameter values needed to perform        authentication with the target network.    -   Obtain local IP address from the target network: This may be        done to obtain a local IP address from the target network that        the mobile can use to receive from IP packets from the target        network.    -   Perform authentication with the target network: This may be done        to perform layer-2, layer-3, and/or application-layer        authentication with the target network if the target network        requires such authentication(s).

In this disclosure, among other actions, the foregoing actions and theaction to establish a connection to a target network as are referred toas types of Handoff Actions.

In some instances, a silent period may be too short for the mobiledevice to perform one or more, or any, handoff action. In thisdisclosure, an Actionable Silent Period (ASP) is defined as a silentperiod that is long enough for the completion of one or more handoffaction(s).

The mobile device may use any existing or new approaches to determinewhether a silent period is expected to be an ASP. For example, a mobilecan treat a silent period as an ASP if the silent period is expected tobe longer than a pre-set (e.g., pre-configured) or dynamicallydetermined threshold. This threshold, referred to as an ASP Threshold,can be different for different handoff actions.

In some embodiments, a dynamic threshold may be determined based on thetimes the mobile device took in the recent past to perform handoffactions. For example, a statistical model can be used to model the timeseries of the times the mobile took to perform handoff actions in therecent past and to estimate the minimum length of time needed to performa handoff action. This minimum time period can then be used as adynamically determined threshold to determine whether a silent periodwill be an ASP.

FIG. 1 illustrates some illustrative basic process steps that may beperformed in some exemplary embodiments of the invention employing asilent proactive handoff approach. While FIG. 1 illustrates somepreferred process steps, it should be appreciated by those in the artbased on this disclosure that the process steps shown in FIG. 1 areillustrative in nature and various embodiments of the invention mayemploy alternative process steps, etc.

With reference to the embodiment shown in FIG. 1, the mobile device caninclude a functional component referred to herein as a silent proactivehandoff processor (SPH Processor) 5, which can, e.g., be configured toperform processing functions of the silent proactive handoffmethodologies. In addition, the mobile device can also include acomponent 6 that includes an algorithm or process to detect if enoughinformation about a candidate network is available, as well as acomponent 7 that includes a mobile speed detection algorithm or process.

FIG. 1 shows some preferred process steps once an SPH processor 5 or thelike initiates the silent proactive handoff process at step 10.

In the preferred embodiments, the mobile device has a functionalcomponent referred to in this disclosure as a Traffic Monitor that isconfigured to monitor the time periods between packets (e.g.,inter-packet times) entering and/or leaving the mobile device over thecurrent access network (i.e., the network the mobile uses currently totransport its application traffic), such as shown at step 20 in FIG. 1.

In the preferred embodiments, the mobile device also includes afunctional component called an ASP Predictor that uses the output fromthe Traffic Monitor and a prediction model to detect the next ASP and topredict its length, such as, e.g., shown at step 40 in FIG. 1. While avariety of known prediction models may be used (as would be understoodby those in the art based on this disclosure), some non-limitingexamples of illustrative prediction models can include Wiener Processmodels and/or time series models, such as, e.g., auto-regression models.

In some embodiments, the ASP Predictor can dynamically estimate the ASPthresholds based on the times the mobile took to perform handoff actionsin the recent past. To dynamically estimate the ASP thresholds, in someembodiments, the ASP Predictor includes components as depicted in FIG.2. In this regard, according to the embodiment shown in FIG. 2, an ASPPredictor 200 includes an ASP Threshold Estimator 210 and an ASPPrediction Model 220 as shown. In some embodiments, the ASP ThresholdEstimator 210 receives as input the times the mobile device took toperform prior handoff actions (such as, e.g., handoff actions within therecent past) as schematically shown as inputs at arrows A1 in FIG. 2. Insome preferred embodiments, the ASP Threshold Estimator 210 can then useany appropriate means (as would be understood by those in the art basedon this disclosure), such as statistical models, to estimate the minimumtime it has recently taken the mobile to perform each handoff action anduse it as the ASP threshold for each handoff action.

In the preferred embodiments, the estimated ASP thresholds can then betransmitted to the ASP Prediction Model 220, such as, e.g., shown atarrow A2 in FIG. 2. Then, the ASP Prediction Model 220 can use thesethresholds and the inter-packet times from the Traffic Monitor (see,e.g., step 20 in FIG. 1) to detect the next silent period (such as,e.g., [T, T+A] from the current time t=T), to predict if this nextsilent period will be an ASP, and to predict the length of the next ASP,such as, e.g., depicted at 220 in FIG. 2 and at 40 in FIG. 1. As shownat A3 in FIG. 2, the ASP Prediction Model 220 preferably outputs a nextpredicted ASP. Then, the mobile device or the SPH processor canpreferably use this information to control silent proactive handoffduring such a next ASP period.

As also shown in FIG. 1, the mobile device also preferably includes afunctional component referred to in this disclosure as a Target NetworkSelector that selects a target network to which the mobile device mayswitch to, such as, e.g., shown at step 30 in FIG. 1. In some preferredembodiments, as shown in FIG. 1, the target network selector operates inparallel to the traffic monitor. In various embodiments, the targetnetwork selection can be based on any criteria deemed appropriate tosatisfy the requirements of the mobile device and the applicationsrunning on the mobile device. These criteria may include, for example,the detection of a new radio network, when the radio signal strength ofthe current network drops to a threshold.

In the preferred embodiments, when a target network is selected and anactionable silent period is detected, the mobile device switches itsradio connection and layer-2 connection to the target network. If itfails to establish a connection to the target network (e.g., if itslayer-2 authentication fails), the target network selector is preferablynotified. At that time, the target network selector will then preferablyproceed to select a new target network. In some embodiments, as shown inFIG. 1, if at step 50 the mobile device fails to establish a connection,then an algorithm can be employed, such as, e.g., shown at 130 thatincrements a network identification value from, for example, “n” to anetwork identification value of “n=n+1”. However, it should beappreciated that such an algorithm can be omitted as long as, forexample, the target network selector can proceed to select anothernetwork.

In the preferred embodiments, after the mobile device connectssuccessfully to the target network, and proceeds through step 50, and ifthe current ASP has not yet expired, the mobile device enters theinformation discovery phase at step 60 to listen to the target network'slayer-2, IP-layer, and/or application-layer advertisement messages tolearn about the necessary information needed to perform handoffs atdifferent protocol layers to the target network. Preferably, if themobile device has already acquired the information it needed about thetarget network, it will pass through or skip this information discoveryphase (referred to as Step 1 in FIG. 1) and go directly to the next step70 as shown in FIG. 1. On the other hand, if the mobile device has notalready acquired the information, it will proceed to enter theinformation discovery phase at step 65.

In the illustrated embodiment, after passing through this step 65 (and,in particular, if the ASP period terminates), the process may move tothe ASP Predictor in order to predict a net actionable silent periodback at step 40 shown in FIG. 1. Then, upon prediction of an appropriateASP (which, e.g., may be predicted in some embodiments based on thehandoff action to be achieved), the system may again continue downwardalong the process steps as discussed above.

In some embodiments, as described further below, a counter C can beemployed in order to evaluate the number of times the process movesaround the loop from step 40, to step 50, to step 60, to step 65 andthrough the counter back to step 40. Among other things, a counter C canhelp to identify if the system is having difficulty achieving a certainhandoff action, such as, e.g., an initial information discovery handoffaction.

Preferably, if the current ASP does not expire after the informationdiscovery phase, the mobile device starts a second handoff action, suchas, for example, to obtain a local IP address from the target network(referred to as Step 2 in FIG. 1). In this regard, a local IP addressfrom a target network may be an IP address the mobile can use toreceive, e.g., unicast packets from the target network. Preferably, ifthe mobile already has a local IP address from this target network, themobile will go directly to the next step as shown FIG. 1 at step 70. Onthe other hand, if the mobile device has not already acquired theinformation, it will proceed to enter this Step 2 handoff action phaseat step 75.

In the illustrated embodiment, after passing through this step 75 (and,in particular, if the ASP period terminates), the process may move tothe ASP Predictor in order to predict a net actionable silent periodback at step 40 shown in FIG. 1. Then, upon prediction of an appropriateASP (which, e.g., may be predicted in some embodiments based on thehandoff action to be achieved), the system may again continue downwardalong the process steps as discussed above.

Preferably, if the current ASP does not expire after the mobile devicemoves through a particular handoff action, such as, e.g., a Step 1 or aStep 2 handoff action, the system will start to perform a next or newhandoff action. For example, if the current ASP does not expire afterthe mobile device moves through the Step 2 handoff action and acquiresand configures itself with a local IP address from the target network,it will preferably start to perform a new handoff action (referred to asStep 3 in FIG. 1), such as, e.g., to perform the necessaryauthentication at the IP and application layers with the target networkif these authentications are required by the target network, such as,e.g., shown at step 80 in FIG. 1. Preferably, if the mobile alreadyauthenticated with or does not require authentication with this targetnetwork, the mobile device will go directly to the next step as shownFIG. 1 at step 90. On the other hand, if the mobile device has notalready acquired the authentication information, it will proceed toenter this Step 3 handoff action phase at step 85.

In the illustrated embodiment, after passing through this step 85 (and,in particular, if the ASP period terminates), the process may return tothe ASP Predictor in order to predict a next actionable silent periodback at step 40 shown in FIG. 1. Then, upon prediction of an appropriateASP (which, e.g., may be predicted in some embodiments based on thehandoff action to be achieved), the system may again continue downwardalong the process steps as discussed above.

Preferably, if the authentications fail (such as, e.g., indicating thatthe mobile may not be allowed to use the target network), the targetnetwork selector is so notified and the target network selector willstart the selection of a new target network.

If after finishing some or all of the above steps, the mobile device isstill not yet ready to handoff into the target network at step 90 (e.g.,if the current network continues to satisfy the mobile's requirements),the mobile device will preferably switch its network connection back tothe current network (i.e., the old network), such as, e.g., shown atstep 110 in FIG. 1.

Since the above process of switching to the target network and thenswitching back to the current or old network can be advantageously doneduring the otherwise silent periods of the mobile device, the switchingcan be effectively transparent to the applications on the mobile deviceand, hence, will avoid interruptions to such applications.

Reference is now made to FIG. 3 which schematically illustrates the useof silent periods for network discovery and for performing proactivehandoff actions according to some preferred embodiments. As shown inFIG. 3, if during one ASP, the mobile device was only able to performone or a subset of the handoff actions, the mobile device can usesubsequent ASPs to perform the remaining handoff actions needed for thetarget network. In this manner, multiple ASPs can be utilized that arenot concurrent in time in some embodiments. For example, during one ASP,the mobile device can discover the necessary information regarding atarget network (e.g., addresses of the IP access router, the IP addressallocation server, and the authentication server). And, for example,during another subsequent ASP (such as, e.g., a next ASP), the mobiledevice can obtain a local IP address from the target network and/or canperform IP or application-layer authentication with the target network.

Preferably, if the mobile device becomes ready for an actual handoffinto the target network (such as, e.g., when the radio signal strengthof the old network has degraded below a threshold), the mobile devicecan proceed to perform the rest of the handoff steps needed to finishthe actual handoff, such as, e.g., shown at step 100 in FIG. 1. In somepreferred embodiments, the mobile device will proceed to perform therest of the needed handoff steps to finish the actual handoff withouthaving to switch back to the old/current interface.

In some preferred embodiments, after each successful handoff action, thetime the mobile device took to perform the handoff action is passed onto the ASP Predictor, which can be later used by the ASP Predictor toestimate a threshold used to determine dynamically whether a silentperiod is an ASP.

Preferably, the mobile device can repeat the process steps (such as,e.g., process steps depicted in FIG. 3) for multiple radio networks.Preferably, at any given time, the mobile device can have one or more(e.g., multiple) target network(s) with which the mobile has completedone or more handoff actions.

As should be understood based on this disclosure, the present silentproactive handoff approach has significant advantages. For example, withthe silent proactive handoff approach, if handoff actions to a targetnetwork fail during silent periods for any reason (e.g., the user is notauthorized to use the target network), there can be essentially noimpact on the applications.

In some instances, a mobile device may traverse a network too quicklyfor the network to be of any practical use for the mobile device user.For example, a vehicle traveling at 75 miles-per-hour may traverse awireless LAN within about 5 seconds when the wireless LAN has a coveragearea of about 150 meters. In such an illustrative case, the mobiledevice may receive no benefit by handing off into this wireless LANwhen, for example, the user application is voice and/or the like.Therefore, there would be no need for the mobile device to perform suchsilent proactive handoff actions for this wireless LAN.

Accordingly, in some preferred embodiments, a mobile device isconfigured to determine when silent proactive handoff may not be needed.Accordingly, in this manner, the mobile device can be adapted to stopthe silent proactive handoff for networks for which silent proactivehandoff is not appropriate. Among other things, stopping the silentproactive handoff when it relates to a network that does not provide anybenefit to the user can help to reduce unnecessary battery consumption,unnecessary use of processing power, etc.

In some preferred embodiments, a software process, referred to in thisdisclosure as a Silent Proactive Handoff Activator (SPH Activator), isimplemented on the mobile device to dynamically determine when toactivate or deactivate the silent proactive handoff. In someillustrative embodiments, some illustrative ways to decide whether torun silent proactive handoff can be to use one or more of the followingparameters:

1). types of user applications, such as, e.g., voice, data, video, etc.;

2). relative speed at which the mobile device is moving; and

3). predicted size (e.g., diameter) of the candidate network(s).

In some illustrative embodiments, the SPH Activator can use some or allof the above parameters (and/or any other appropriate parameters aswould be apparent to those in the art based on this disclosure) toestimate the time it will take for the mobile device to traverse acandidate network. Preferably, if the estimated traversal time is lowerthan a threshold level φ that represents the minimum amount of time amobile device has to stay inside a network for the network to be usefulfor the user's applications, the SPH Activator stops the silentproactive handoff. On the other hand, if the estimated network traversaltime is higher than the threshold level Φ, then the SPH Activator canpreferably enable and/or start the silent proactive handoff.

To estimate the time it takes a mobile device to traverse a network, themobile device can, in some instances, estimate its moving speed anddirection. In some embodiments, a mobile device's moving speed anddirection can be estimated using one or more of the following methods:

-   -   1). The amount of time that the mobile device took to traverse        similar types of networks in the recent past can be recorded.        For example, IEEE 802.11 networks have similar coverage ranges.        Therefore, the mobile device can estimate the time it will spend        in the next 802.11 network based on the times it spent in other        802.11 networks in the recent past. For example, if the        predicted resident time is shorter than a threshold level Φ, the        mobile can stop the silent proactive handoff for the next 802.11        network.    -   2). A counter C can be evaluated. In this regard, in some        exemplary embodiments, as discussed briefly above, if the value        of a counter reaches reasonably high in a fairly short interval        of time without gathering even the first handoff action        information, that can potentially demonstrate, among other        things, that the mobile device is moving at fairly high speed        and the silent proactive handoff algorithm may be stopped for        some duration to save the battery power. In some embodiments,        the value of this counter C could be hard fixed or may change        dynamically based on some mathematical model. For example, a        statistical or an exponential model could be used to model the        instances that the mobile device tried but failed to get the        first handoff action information in the recent past and could        use this to estimate the minimum length of time on the mobile        device to determine when to re-activate the SPH. By way of        example, in some illustrative embodiments, a counter C could be        procedurally located at the component C as shown in FIG. 1.    -   3). The MAC (Media Access Control) layer signals in most radio        networks allow a mobile to determine when it will receive the        next radio beacon from a certain network. For example, an IEEE        802.11 Basic Service Set (BSS), which is a set of Access Points        that form a local area wireless network, typically sends beacons        in 100 ms intervals. If the mobile receives all the consecutive        beacon signals at regular time intervals, such as for example at        (100.+ΔT) ms where ΔT is the beacon transmission time from an        access point to the mobile, it indicates that the mobile device        is stationary when ΔT is a constant. On the other hand, if ΔT is        decreasing, it means the mobile is traveling in the direction of        the AP from which the radio beacon is received. On yet the other        hand, if ΔT is increasing, it means the mobile is going away        from that access point that is sending the beacons. Thus, in        some embodiments, the rate at which ΔT increases or decreases        can therefore be the predictor of the mobile device's speed as        well as its direction. Thus, in some embodiments, using the        mobile device's estimated moving speed and the estimated        coverage range of a network, the mobile device can estimate the        time it will take to go through the network.

In some embodiments, the foregoing predictor can also be used to downselect the candidate networks. In particular, networks that the mobiledevice is moving closer to can receive higher preference than networksthat the mobile device is moving farther away from, when the mobiledevice decides which candidate networks to select to perform proactivehandoff processing.

In some embodiments, a decision to stop or to continue to run the ASPalgorithm can also be made if the gathered information about thecandidate networks is sufficient. That is, if the information collectedabout the available networks is already enough, in some embodiments, thealgorithm can be stopped from gathering further information.

FIG. 4 shows an illustrative, and non-limiting, architecture of anexemplary mobile device 400 having silent proactive handoffcapabilities. As shown, in some preferred embodiments, the mobile device400 includes application functionality 410, IP layer functionality 420,a traffic monitor 430, a radio network interface card 440, a policydatabase 450, a silence predictor 460, a target network selector 470,and a silent handoff controller 480. As also generally indicated in FIG.4, the radio network interface card of the mobile device can connect toan Access Point or the like within one of the networks N1, N2 and N3 inthe illustrated example.

In the illustrated example, the functional entity or component referredto as the silent handoff controller 480 implements the functionality themobile device performs during an actionable silent period, such as:

-   -   establishing connections to a target networks;    -   discovering network information about the target networks;    -   obtaining local IP address from the target networks; and/or    -   performing the require authentications with the target networks.

In various embodiments, the functions incorporated as part of the silenthandoff controller 480 could be implemented in hardware, firmware and/orsoftware and/or could also be implemented in, e.g., separate softwareentities.

In the preferred embodiments, a policy database 450 is provided thatmaintains user policies regarding how different networks should be used.As some illustrative and non-limiting examples, a policy may specify oneor more of the following: a) that a wireless LAN is always preferredover a cellular network; b) that a wireless LAN is always preferred overa cellular network for voice applications; c) that a network with ahigher signal strength is always preferred; d) that a network ispreferred if it can provide a higher available bandwidth or lower delay;and/or e) other policy specifications.

In the embodiment shown in FIG. 4, a traffic monitor 430 is preferablyimplemented as a layer between the IP layer 420 and the network devicedrivers 440. In other embodiments, a variety of other ways ofimplementing a traffic monitor 430 can be used. By way of example, atraffic monitor could be an application process that obtains trafficinformation by polling the device drivers or by periodically receivingtraffic information from the device drivers.

As indicated above, the various functional components of the mobiledevice can be implemented in a variety of ways, as would be understoodby those in the art based on this disclosure. For example, some or allof the functional components can be implemented in software at theapplication layer and/or at the kernel layer. Additionally, some or allof the functional components can be implemented in hardware, firmwareand/or on micro-chips.

Thus, as depicted in the exemplary system shown in FIG. 5 forillustrative purposes only, a mobile device (e.g., mobile station) MScan begin inside the radio coverage of a first network N1 having anaccess point AP1 at a position A. Then, upon moving into a position B,the mobile device MS can simultaneously be situated within the radiocoverage of a second network N2 and a third network N3, havingrespective access points AP2 and AP3. As a result, in this region B, themobile device can perform silent proactive handoff functionality asdescribed above (e.g., performing handoff actions during silent periodswhile the mobile station is still satisfied by the network N1), suchthat upon a later movement of the mobile device MS to the position C, avery fast handoff can be achieved (e.g., from network N1 to either ofnetwork N2 or N3 in the illustrated exemplary path).

BROAD SCOPE OF THE INVENTION

While illustrative embodiments of the invention have been describedherein, the present invention is not limited to the various preferredembodiments described herein, but includes any and all embodimentshaving equivalent elements, modifications, omissions, combinations(e.g., of aspects across various embodiments), adaptations and/oralterations as would be appreciated by those in the art based on thepresent disclosure. The limitations in the claims are to be interpretedbroadly based on the language employed in the claims and not limited toexamples described in the present specification or during theprosecution of the application, which examples are to be construed asnon-exclusive. For example, in the present disclosure, the term“preferably” is non-exclusive and means “preferably, but not limitedto.” In this disclosure and during the prosecution of this application,means-plus-function or step-plus-function limitations will only beemployed where for a specific claim limitation all of the followingconditions are present in that limitation: a) “means for” or “step for”is expressly recited; b) a corresponding function is expressly recited;and c) structure, material or acts that support that structure are notrecited. In this disclosure and during the prosecution of thisapplication, the terminology “present invention” or “invention” may beused as a reference to one or more aspect within the present disclosure.The language present invention or invention should not be improperlyinterpreted as an identification of criticality, should not beimproperly interpreted as applying across all aspects or embodiments(i.e., it should be understood that the present invention has a numberof aspects and embodiments), and should not be improperly interpreted aslimiting the scope of the application or claims. In this disclosure andduring the prosecution of this application, the terminology “embodiment”can be used to describe any aspect, feature, process or step, anycombination thereof, and/or any portion thereof, etc. In some examples,various embodiments may include overlapping features. In thisdisclosure, the following abbreviated terminology may be employed:“e.g.” which means “for example.”

1. A method for performing silent proactive handoff of a mobile deviceto a target network while the mobile device is using a current network,comprising: while the mobile device is using the current network totransport application traffic and the current network satisfies themobile device's requirements, having the mobile device use at least onesilent period to temporarily connect to at least one target network toproactively perform at least one handoff action for potential laterhandoff to the target network.
 2. The method of claim 1, wherein saidmobile device sends or receives substantially no traffic over thecurrent access network during the at least one silent period.
 3. Themethod of claim 1, further including having the mobile device use the atleast one silent period to connect to the target network so that themobile device receives advertisement messages from the target network.4. The method of claim 1, further including having the mobile device usethe at least one silent period to establish a layer-2 connection orassociation with the target network for receiving IP-layer or high layeradvertisements from the target network.
 5. The method of claim 1,further including having the mobile device use the at least one silentperiod to perform layer-2, layer-3 or application layer authenticationwith the target network.
 6. The method of claim 1, further includinghaving the mobile device perform the following handoff actions duringthe at least one silent period: a) discovering neighboring networkinformation; b) obtaining a local IP address from the target network;and c) performing authentication with the target network.
 7. The methodof claim 1, further including having the mobile device determine if theat least one silent period is sufficient to complete one or more handoffaction.
 8. The method of claim 1, further including having the mobiledevice determine if the at least one silent period is sufficient tocomplete one or more handoff action by comparison to a pre-set or adynamically determined threshold.
 9. The method of claim 8, furtherincluding comparing different threshold values for different handoffactions.
 10. The method of claim 1, further including the mobile devicemonitoring time periods between packets entering and/or leaving themobile device over the current access network that the mobile devicecurrently uses to transport its application traffic.
 11. The method ofclaim 1, further including having the mobile device predict anactionable silence period based on said monitoring of time periods and aprediction model.
 12. The method of claim 1, further includingdynamically estimating at least one actionable silence period thresholdfor at least one handoff action based on previous times the mobiledevice took to perform handoff actions, using the at least one thresholdand inter-packet times determined from a traffic monitor to detect anext silent period, to predict if this next silent period will be anactionable silent period, and to predict a length of the next actionablesilent period.
 13. The method of claim 1, further including having saidmobile device select a target network to which the mobile may switch to.14. The method of claim 13, further including when a target network isselected and an actionable silent period is detected, switching themobile device's layer-2 connection to the target network.
 15. The methodof claim 1, further including having the mobile device connectsuccessfully to the target network and before a current actionablesilent period expires, having the mobile device enter an informationdiscovery phase to listen to the target network's advertisement messagesto learn information needed to perform handoffs at different protocollayers to the target network, and if the current actionable silentperiod has not expired after the information discovery phase, having themobile device start at least one handoff action.
 16. The method of claim15, further including after having the mobile device start said at leastone handoff action, in the event that the current network continues tosatisfy the mobile device's requirements, having the mobile deviceswitch its network connection back to the current network.
 17. Themethod of claim 15, further including after having the mobile devicestart said at least one handoff action, in the event that the currentnetwork does not continue to satisfy the mobile device's requirements,having the mobile device perform the remaining handoff steps to finish ahandoff.
 18. The method of claim 1, further including having said mobiledevice make a determination as to whether to utilize a silent proactivehandoff based on an estimation of the time that the mobile device willbe within a candidate network.
 19. The method of claim 18, furtherincluding having said mobile device make said determination based on oneor more of the following parameters: types of user applications;relative speed at which the mobile device is moving; and a predictedsize of a candidate network.
 20. A mobile device having silent proactivehandoff capability, comprising: a) a traffic monitor componentconfigured to monitor time periods between packets transmitted to orfrom the mobile device over a current access network; b) a targetnetwork selector component configured to select a target network towhich the mobile device may potentially switch to; c) a silencepredictor component configured to predict an actionable silence period;and d) a silent handoff controller configured to control a silentproactive handoff to a target network during the actionable silentperiod.
 21. The mobile device of claim 20, wherein said silent handoffcontroller is configured to establish connections to a target network,to discover network information about a target network, to obtain alocal IP address for the mobile device from the target network, and toperform authentication with the target network.